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The Hubble Space Telescope is an iconic observatory, a triumph of space science that may be the most famous unmanned spacecraft since Sputnik. Hubble's renown is certainly well-deserved, but the spacecraft is aging—it will mark its 20th anniversary of reaching orbit in April. Hubble's services are still in tremendous demand, because it operates above the bulk of Earth's obfuscating atmosphere and so offers astronomers their clearest view of the distant universe. In 2014, when another large, space-borne observatory is set to be launched, the overworked Hubble should finally have some company.

Named for NASA's second administrator, who led the agency during the development of the Apollo program, the James Webb Space Telescope (JWST) will dwarf its predecessor by most measures. (The project is a collaboration among NASA and the European and Canadian space agencies.) Nearly twice as long as Hubble, and boasting a light-collecting mirror several times larger, JWST will also venture farther afield than its elder counterpart. Whereas Hubble circles Earth at an altitude of less than 600 kilometers, JWST will set up shop 1.5 million kilometers away, well beyond the orbit of the moon.

During a February lecture at the American Museum of Natural History in New York City, Jon Arenberg of Northrop Grumman, the prime contractor on the project, presented an overview of the telescope's mission and an update on its developmental progress as JWST moves from the design phase to construction and testing. Arenberg, Northrop Grumman's deputy for JWST systems engineering, paid special attention to the challenges inherent in building such a massive and complex machine—and then folding it into a rocket's cramped payload capsule.

Read about some of those design challenges—and some of the remarkable feats that JWST should be capable of—in a slide show of images from the telescope's construction.